I'm trying to decompile the source code with MCP (read only). So far so good it worked with decompiling the Client, however I cannot get the Server decompiling to work. When I'm adding the server.jar to the jars folder and run decompile.bat, it throws the messages in the title.

First !! Modified jar detected. Unpredictable results !! (which isn't thrown when I only decompile Client), followed by a stacktrace of errors ending with Initial server recompile failed, correct source then run updatemd5. (Also read online that the stacktrace itself is not necessarly bad)

I tried everything I found so far but nothing was a success.

Things I tried:

Allocated more ram in mcp.cfg

Fresh Minecraft 1.15.2 and 1.12 (1.15.2 going by their github should be supported)

Newest server (1.15.2) as well as 1.12 server

Server name "server.jar", "minecraft_server.jar" and "minecraft_server.1.12.jar"

Reinstalled MCP

Running on jdk1.8 and jre1.8. Tutorials online said to only download the jdk, but the README-MCP.TXT says to use both.